Lactose intolerance happens when the small intestine is not able to digest lactose. Lactose is a type of sugar found in milk and other dairy products.
The reason for this problem is that the intestine does not make enough of the enzyme lactase. Enzymes help the body absorb foods. Not having enough lactase is called lactase deficiency.
Lactase deficiency; Milk intolerance; Disaccharidase deficiency; Dairy product intolerance
Causes, incidence, and risk factors
Babies' bodies make the lactase enzyme so they can digest milk, including breast milk.
Premature babies sometimes have lactose intolerance. Children who were born at full term usually do not show signs of lactose intolerance until they are at least 3 years old.
Lactose intolerance is very common in adults and is rarely dangerous. About 30 million American adults have some amount of lactose intolerance by age 20.
- In Caucasians, lactose intolerance usually affects children older than age 5.
- In African Americans, it often occurs as early as age 2.
- Lactose intolerance is normal among adults with Asian, African, or Native American heritage.
- It is much less common in people of northern or western European ancestry.
Other causes of lactose intolerance include:
- Bowel surgery
- Infections in the small intestine from viruses, bacteria, or parasites (most often seen in children, but can also occur in adults)
- Intestinal diseases such as celiac sprue
Symptoms often occur 30 minutes to 2 hours after you eat or drink milk products, and are often relieved by not eating or drinking milk products. Large doses of milk products may make symptoms worse.
- Abdominal bloating
- Abdominal cramps
- Gas (flatulence)
Signs and tests
Other intestinal problems, such as irritable bowel syndrome, may cause the same symptoms as lactose intolerance.
Tests to help diagnose lactose intolerance include:
- Lactose-hydrogen breath test
- Lactose tolerance test
- Stool pH
Most people with low lactase levels can drink 2 - 4 ounces of milk at one time (up to one-half cup) without having symptoms. Larger (more than 8 oz.) servings may cause problems for people with lactase deficiency.
These milk products may be easier to digest:
- Buttermilk and cheeses (they have less lactose than milk)
- Fermented milk products, such as yogurt
- Goat's milk
- Ice cream, milkshakes, and aged or hard cheeses
- Lactose-free milk and milk products
- Lactase-treated cow's milk for older children and adults
- Soy formulas for infants younger than 2 years
- Soy or rice milk for toddlers
You can add lactase enzymes to regular milk, or take these enzymes in capsule or chewable tablet form.
Not having milk in your diet can lead to a shortage of calcium, vitamin D, riboflavin, and protein. You may need to find new ways to get calcium into your diet (depending on your age and gender, you need 1,000 - 1,500 mg of calcium each day):
- Take calcium supplements
- Eat foods that have more calcium (leafy greens, oysters, sardines, canned salmon, shrimp, and broccoli)
- Drink orange juice that contains added calcium
Read food labels. Lactose is also found in some non-milk products -- including some beers.
Symptoms usually go away when you remove milk products and other lactose containing products from your diet. Infants or children may grow more slowly or lose weight without changing their diet.
Calling your health care provider
Call your health care provider if:
- You have an infant younger than 2 or 3 years old who has symptoms of lactose intolerance.
- Your child is growing slowly or not gaining weight.
- You or your child has symptoms of lactose intolerance and you need information on food substitutes.
- Your symptoms get worse or do not improve with treatment, or you develop new symptoms.
There is no known way to prevent lactose intolerance.
Hogenauer C, Hammer HF. Maldigestion and malabsorption. In: Feldman M, Friedman LS, Sleisenger MH, eds. Sleisenger & Fordtran's Gastrointestinal and Liver Disease. 9th ed. Philadelphia, Pa: Saunders Elsevier; 2010: chap 101.
Lactose intolerance. The National Digestive Diseases Information Clearinghouse (NDDIC). NIH Publication No. 09-2751. June 2009.
Semrad CE. Approach to the patient with diarrhea and malabsorption. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 142.